Polyatomic MO Recipe Formaldehyde, H2CO (Localized π Bond)

[TP] In formic acid, HC(O)OH, the hybridization on the O single-bonded to the C is (use the Lewis structure) … 25% 25% 25% 25% 1. 2. 3. 4. none sp sp2 sp3 • Polyatomic MO recipe: Formaldehyde, H2CO (localized π bond) • Formic acid, HC(O)OH (localized π bonds) • Formate, HC(O)O− (delocalized π bonds) 1 Polyatomic MO recipe Polyatomic MO recipe: Formaldehyde, H2CO 1. Use Lewis structure to determine the number of (valence) electron pairs and hybridization on each atom. 2. Construct the σ framework of σ bonding and σ nonbonding MOs, and fill each of these MOs with a single pair of electrons. 3. From the p AOs not used in the σ framework, construct the π framework of π bonding, nonbonding, and antibonding MOs, and use the relative energies to fill each of these MOs with a single pair of electrons. 1. Use the Lewis structure to get … • the number of electron pairs • make hybrid AO’s on each central atom; terminal atoms (except H) have same hybrid AO’s as their central atom 3 4 1 Polyatomic MO recipe: Formaldehyde, H2CO Formaldehyde, H2CO, σ framework 1. Use the Lewis structure to get … • the number of electron pairs • make hybrid AO’s on each atom; terminal atoms (except H) have same hybrids as central atom 2. Sketch the σ (MO) framework and place pairs … • in each bonding σ MO • in each nonbonding hybrid AO 6 pairs in Lewis structure, 5 pairs in σ framework, and so 1 pair in (localized) π framework. 5 Formaldehyde, H2CO, σ framework 6 H2CO sp2 σ framework 6 pairs in Lewis structure, 5 pairs in σ framework, and so 1 pair in (localized) π framework. 6 pairs in Lewis structure, 5 pairs in σ framework, and so 1 pair in (localized) π framework. 7 8 2 Polyatomic MO recipe: Formaldehyde, H2CO H2CO π framework 1. Use the Lewis structure to get … • the number of electron pairs • make hybrid AO’s on each atom; terminal atoms (except H) have same hybrids as central atom 2. Sketch the σ framework and place pairs … • in each bonding σ MO • in each nonbonding hybrid AO 3. Sketch the π framework MO’s: • mark as bonding, nonbonding, and antibonding • place remaining pairs (Auf Bau) • get the π bond order 9 10 H2CO π framework 1 pair in (localized) π framework 1 pair in π (bonding); bond order 1 Formic acid, HC(O)OH 11 12 3 [TP] In formic acid, HC(O)OH, the hybridization on the O single-bonded to the C is (use the Lewis structure) … 25% 25% 25% 25% 1. 2. 3. 4. [Quiz] In formic acid, HC(O)OH, the hybridization on the O double-bonded to the C is (use the Lewis structure) … none sp sp2 sp3 25% 25% 25% 25% 1. 2. 3. 4. none sp sp2 sp3 13 HC(O)OH π framework HC(O)OH σ framework • • • • 14 1 pair in (localized) π framework Hybridization of terminal atoms the same as their central atom Terminal H never hybridized One pair in each hybrid AO σ bonding MO One pair in each non-bonded hybrid AO 16 1 pair in π (bonding); bond order 1 19 4 [TP] Formic acid, HC(O)OH, and it conjugate base formate, HC(O)O−, each have 9 pairs of electrons. How many pairs of electrons are in the σ framework of formate? Formate, HC(O)O‒ 20% 20% 20% 20% 20% 1. 2. 3. 4. 5. 3 pairs 5 pairs 7 pairs 8 pairs 9 pairs 20 HC(O)O‒ sp2 σ framework 21 HC(O)O‒ sp2 σ framework 9 pairs in Lewis structure, 7 pairs in σ framework, and so 2 pairs in (delocalized) π framework. 22 23 5 [TP] How many pairs of electrons are in the π framework of formate? 25% 25% 25% 25% 1. 2. 3. 4. HC(O)O− π framework 0 pairs 1 pairs 2 pairs 3 pairs 24 25 HC(O)O− π framework 2 pairs in (delocalized) π framework 1 pair in π (bonding) and 1 pair in πn (nonbonding); bond order 1 26 6